New user!

[GaWd]

TIred of the Trolls on the Usenet, and I happened by this forum. On to my question...

88 K1500 350cid engine, 88k miles.

Having pedal problems...very inconsistant. Today I flushed and bled the brakes and the master. GOt the air out of the system, no brake warning light on. Bled at brake line connectors, wheel cyls, and the bleed valve on the master.

After the bleeding and flushing, I still have the same problem. Too much travel at times, nice pedal sometimes, and sometimes too hard.

Any ideas?

TIA,

Sam

[ThreeQuarter]

Sam, welcome to the board!

Let's see here...a bleed valve on the master cylinder? Do you have a pic, or a more specific description of it?

Usually if the pedal effort is soft you need a master cyilnder, and if it's hard, you need a power booster. Too much travel tells me it's the MC or it still has some air in the system, regardless of the amount of boost. But then GM always did put a lot of travel in the brakes pedals before they actually started braking. Have you checked the vaccuum hose to the booster? Is the vaccuum source constant, or does it fluctuate? Let me know.

Ben

[GaWd]

Thanks, GMC.

THe vacuum line is good, and crack-free. The fitting appears a touch loose, but I can't hear vacuum escaping.

There is a bleeder on the top of the master cylinder. I believe the FSM calls it the Isolation/Dump Valve.

How do you reset the rear self-adjusters? I've been told it is done by accellerating in reverse and applying pressure to the pedal, but not locking them up.

Anything I've missed? Would it be prudent to see if the brake system is throwing codes?

Thanks again,

Sam

[Zkast]

The diagnostics on the early style Teves IV antilock system was all but a joke. The codes are very vague being that there were only 9 possibilities.

Did this problem start before or after bleeding the brakes?
Physically check the adjustement of the rear brakes. This will cause a very inconsistant pedal height/feel. Once you have checked and adjusted the rear brakes I would try bleeding once more. Start with the mastercylinder bleed valve/ dump valve then bleed the furthest wheel from the M/C and work your way in. Right rear/Left Rear/Right front/Left front.

At this point you 'know' there is no air in the system. Dont rule out the possibility of a bad master cylinder though.... But GM has a terrible design on the RWAL system of these trucks/SUV's. The dump valve is the cause of most "soft spongy" pedals. I've seen vehicles come into the shop where people have removed/bypassed this dump valve to obtain a VERY high and tight pedal again. Of course this disables the RWAL unit and usually will not cause the abs light to come on.

If worse comes to worse you can purchase a set of brass block off plugs which will allow you to isolate each componant and find out where your excessive fluid travel is going. 75% of the time we find a weak dump valve spring.

Good luck with it.

[GaWd]

Ok, pretend I'm an idiot, how do you go about adjusting brakes with self-adjusters? How tight should they be, and/or, how much drap upon freely spinning the tire?

I'm sure it's the rears throwing the whole system off kilter, I'm just looking for another opinion. THe truck has driven like this for many years(!), so this is not a new problem. I just purchased it from my fiancee's family, so I know the history pretty well.

Thanks again,

Sam

[ThreeQuarter]

You can adjust them w/out taking off the wheels, but I'd want to get a good look a the brakes, so I would take the wheels and drums off and turn the little "star" that spreads the shoes until the drum slides on tight. And then back of a few notches. This will help if they're waaaaay out of adjustement, since it takes a lot of backing up and stopping to get anywhere with the self-adjusters. Self adjusting only goes a couple or three clicks per stop.

As far as bleeding the M/C goes, I'll defer to Zkast since I've never bled through a dump valve before. However, I think the left rear brakes are farther out down the line from the M/C than the right rears. If you look at the T-junction on the axle, it is closer to the right, so I'd start bleeding on the LR, then RR, RF, LF. Bleeding is no fun, but good luck!